Technological advances in recent years have made it easier for individuals and groups in geographically disperse societies to be interconnected through physical travel and communication systems. Major advances in the telecommunications infrastructure have been developed and are continuously evolving to meet the needs of people who regularly travel, communicate, and do business internationally. For example, satellite-based global communication networks have arisen to serve the needs of global travelers and communicators. One such network, first activated in 1998, is the Iridium® commercial system. The Iridium® commercial system is a satellite-based global digital communication network designed to provide wireless communications through hand-held devices located anywhere near or on the surface of the Earth.
FIG. 1 illustrates a highly simplified diagram of a satellite-based communication network 20, dispersed over and surrounding Earth through the use of orbiting satellites 22 occupying orbits 24. Network 20 uses six polar orbits 24, with each orbit 24 having eleven satellites 22 for a total of sixty-six satellites 22. As such, network 20 exemplifies the Iridium® commercial system.
Satellites 22 communicate with radio communication individual subscriber units (ISU's) 26 over subscriber links 28. In addition, satellites 22 communicate with earth terminal/gateway systems 30, which provide access to a public switched telephone network (PSTN) 32 or other communications facilities, over earth links 34. Earth terminal/gateway systems 30 (referred to hereinafter as gateways 30) relay data packets (e.g., relating to calls in progress) between ISU's 26 and the PSTN 32 to other communication devices, such as a wireline telephone 36. Satellites 22 also communicate with other nearby satellites 22 through cross-links 40. For simplicity of illustration, only one each of ISU's 26, gateways 30, and a wireline telephone 36 are shown in FIG. 1.
With the exemplary constellation of sixty-six satellites 22, at least one of satellites 22 is within view of each point on the Earth's surface at all times, resulting in full coverage of the Earth's surface. Any satellite 22 may be in direct or indirect data communication with any ISU 26 or gateway 30 at any time by routing data through the constellation of satellites 22. Accordingly, communication network 20 may establish a communication path for relaying information through the constellation of satellites 22 between any two ISU's 26, or between ISU 26 and gateway 30.
Network 20 may accommodate any number, potentially in the millions, of ISU's 26. Subscriber links 28 encompass a limited portion of the electromagnetic spectrum that is divided into numerous channels, and are preferably combinations of L-Band frequency channels. Subscriber links 28 may encompass one or more broadcast channels 42, that ISU's 26 use for synchronization and message monitoring, and one or more acquisition channels 44 that ISU's 26 use to transmit messages to satellites 22. Broadcast channels 42 and acquisition channels 44 are not dedicated to any one ISU 26 but are shared by all ISU's 26 currently within view of a satellite 22.
Subscriber links 28 also include wireless traffic channels 46, also known as voice channels. Traffic channels 46 are two-way channels that are assigned to particular ISU's 26 from time to time for supporting real-time communications. Each traffic channel 46 has sufficient bandwidth to support a two-way voice communication. For example, each of traffic channels 46 within the Iridium® network are capable of approximately 2.4 kilobits/second (kbps) raw data throughput.
Techniques are being developed to utilize such satellite-based networks to transmit large data files and real-time video, in addition to voice communications. Such a technique is described in the aforementioned related invention, “System And Method For Satellite-Based Transmission Of Signals Using Multiple Channels,” U.S. patent application Ser. No. 10/404,791. The technique extends the capability of voice optimized traffic channels, within a wireless communication system, for the transmission of data and video.
Even though the technique enables the transmission of data and video over voice optimized traffic channels, a need has arisen for a system and method for effectively enabling voice signal transmission over data and video transmission. More particularly, due to the real-time nature of voice transmissions, voice signal transmission should supersede the data and/or video in the event of a current transmission of data and/or video.